The physiological passageways and cavities of human and animal bodies, for example, blood vessels and ducts, occasionally weaken or even rupture. One common surgical intervention for weakened, aneurysmal or ruptured passageways or ducts involves the use of an endoluminal prosthesis to provide some or all of the functionality of the original, healthy passageway or duct and/or preserve any remaining vascular integrity by replacing a length of the existing passageway or duct wall that spans the site of failure or defect. Endoluminal prostheses may be of a unitary construction or may be comprised of multiple prosthetic modules.
Delivery catheters or sheaths are widely used for the delivery of a stent or a stent graft to a deployment site well within the vasculature of the patient. Typically, the delivery catheter is inserted over a guide wire. In one common arrangement, used particularly with self-expanding stents, an inner core carries the stent and has a distal tip that is atraumatic and may assist in dilating the vessel as the delivery catheter advances along the guide wire. A sheath covers the stent during the delivery procedure and maintains or assists in maintaining the stent in its radially compressed configuration. The distal tip will usually have a smooth outer surface, tapering axially from a relatively large outer diameter, corresponding to the outside diameter of the sheath, to a relatively small outer diameter at the distal end of the sheath, corresponding (with an appropriate wall thickness for the tip) to the outside diameter of the wire guide. Once the stent has reached the deployment site, the sheath is withdrawn, uncovering the stent and allowing it to expand radially.
When endoluminal prostheses or antistenotic stents are implanted to treat these or similar conditions, it is important that they do not migrate under physiological forces. Pulsatile flow is a major force that stents encounter, thus stents and endoluminal prostheses tend to move downstream in the blood vessel. If the stents or endoluminal prosthesis migrate, they can travel beyond the length of the vessel they are intended to treat. For example, if an antistenotic stent migrates, it will fail to keep the targeted portion of the vessel from restenosing. Accordingly, the endoluminal prosthesis may include an attachment stent disposed on an end portion thereof. The attachment stent may comprise a plurality of barbs that in use are adapted to anchor the prosthesis to a surrounding body lumen. An end portion of the attachment stent is retained within the delivery device by a cover, or a top cap, in order to keep the attachment stent in a radially constrained state. To deploy the prosthesis, the operator withdraws the top cap from the attachment stent, thereby exposing the stent and allowing it to expand radially outwardly.
The stent radially expands against an inner surface of the top cap prior to deployment. The expansion force of the stent against the inner surface can be sufficiently high so as to create significant interference between the stent and the top cap. This can result in increased operating effort to remove the cover from the stent. This is particularly true where the stent comprises sharpened barbs that may scratch or dig into the inner surface of the top cap.